Pressure sensitive adhesives (PSA) are well known and are used in many industrial, consumer and medical applications. Pressure sensitive adhesives are formulations typically comprising an elastomeric polymer, a tackifier, and optionally an oil or other additives. These adhesives remain permanently tacky and adhere instantaneously to a wide variety of surfaces with the application of a small amount of pressure. Pressure sensitive adhesives are generally used in the form of a coating on a backing, such as in adhesive bandages, wound dressings, transdermal delivery devices, tapes, stencils, wall paper, envelopes, stamps, and floor tiles.
For many applications, it is desirable to be able to remove the adhesive from the surface without significant force, so that the surface, for example, newly healed skin, is not damaged. For this reason, switchable adhesives, which undergo a reduction in peel strength with a change in conditions, have been developed. Switchable adhesives that exhibit a reduction in peel strength upon contact with water or exposure to UV radiation are known. Additionally, temperature switchable adhesives, which undergo a reduction in peel strength with a temperature change have also been reported.
Stewart in U.S. Pat. Nos. 5,156,911 and 5,387,450 describes a temperature switchable adhesive composition comprising a side chain crystallizable polymer. The adhesive is nontacky, or slightly tacky at room temperature, but is aggressively tacky at skin temperature. Therefore, the adhesive may be removed from the skin by cooling.
Schmitt et al. in U.S. Pat. No. 5,412,035 describe pressure sensitive adhesive compositions, containing a crystalline polymeric additive, that lose adhesive strength upon heating. The crystalline polymeric additive is preferably a side chain crystallizable polymer having a weight average molecular weight of less than 25,000.
The aforementioned temperature switchable adhesives provide the desirable property of losing adhesive strength with a change in temperature. However, it is difficult to adjust the temperature switchable properties of those adhesive compositions because a different crystallizable side chain polymer and monomer must be synthesized to meet different switching temperature requirements.
The use of abietic acid in the form of natural rosin, and the glycerin ester and the pentaerythritol ester of hydrogenated rosin, as a tackifier in pressure sensitive adhesives is known (Ito et al, U.S. Pat. No. 4,421,737). Additionally, the hexadecyl ester of abietic acid and its use as a plasticizer for polyvinyl chloride is described by Szczepanik et al. (Polish Patent No. 144242). However, the use of abietic acid derivatives having crystallizable groups as tackifiers for temperature switchable adhesives has not been reported.
In view of the above, the need exists for new temperature switchable adhesives for which the temperature switching properties may be readily adjusted to meet the requirements for many different applications by readily changing the tackifier and elastomer used in the formulation, according to standard principles of adhesive formulation.
Applicants have addressed the stated need by discovering that certain abietic acid derivatives having crystallizable groups may be used as a tackifier to give new temperature switchable pressure sensitive adhesive compositions. The adhesive properties of these adhesives may be readily tuned to meet the requirements of various applications.